Roofing membrane and method of forming same

ABSTRACT

A roofing membrane is provided including a weft insertion warp knit fabric substrate having continuous filament warp yarns of polyester, polyamide or other suitable synthetic material, continuous filament weft yams of the same or different synthetic material as the warp yams, the warp yams and/or weft yams having a predetermined twist therein, and knit yams warp knit in a chain stitch pattern binding the warp and weft yams together.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of provisional patent application Serial No. 60/316,143 filed on Aug. 30, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to roofing membranes for commercial roofing applications and more particularly to single-ply roofing membranes.

BACKGROUND OF THE INVENTION

[0003] The commercial roofing industry utilizes roofing membranes consisting of substrates coated with coatings used in the roofing industry. Such substrates may be of various constructions, one of the most commonly used constructions being a weft insertion warp knit fabric. Heretofore, these weft insertion warp knit fabrics have consisted of a warp of continuous filament yams of synthetic material, e.g. polyester, nylon or fiberglass, and a weft of continuous filament yams of synthetic material inserted perpendicularly to the warp yams. The warp and weft yams are bound together by warp knit stitches which penetrate through the banks of warp and weft yams.

[0004] These previously used weft insertion warp knit fabrics have utilized warp and weft yams having zero twist and a tricot stitch pattern for the warp knit stitches. Such prior weft insertion warp knit fabrics have at least two marked deficiencies or disadvantages. Firstly, the tricot stitch pattern results in curled selvages in the weft insertion warp knit fabrics in the greige state and, when coated, the curled selvages manifest into wavy edges causing poor lay flat and uneven seams or joints, all of which are very undesirable in roofing structures. Secondly, the tear strength is inadequate for wind uplift loads generated by wider roofing membranes. Also, the tear strength varies significantly in such prior weft insertion warp knit fabrics due at least in part to the different methods of manufacture, such as extrusion coating, calendar coating, film lamination, etc. Since the trend in the roofing industry is toward the use of wider roofing membranes and the wider the membrane the greater the wind uplift load, the need for greater and more uniform tear strength has become acute.

BRIEF SUMMARY OF THE INVENTION

[0005] With the foregoing in mind, it is an object of the present invention to provide a roofing membrane and an improved weft insertion warp knitted fabric therefore and method of forming the same which obviate the aforementioned deficiencies and disadvantages. This object is accomplished by forming a weft insertion warp knitted fabric from a bank of continuous filament warp yams of synthetic material and a bank of weft yams of continuous filament synthetic material bound together by warp knitting in a chain stitch pattern. The warp yams and/or weft yams may have a predetermined twist therein sufficient to provide increased and substantially uniform tear strength in the weft insertion warp knit fabric. The chain stitch pattern in the warp knit obviates curled selvages in the greige state and wavy edges when coated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0007]FIG. 1 is a plan view of a weft insertion warp knit fabric incorporating the present invention;

[0008]FIG. 1A is an enlarged fragmentary view of the fabric illustrated in FIG. 1;

[0009]FIG. 2 is a view similar to FIG. 1A of another embodiment of the fabric of the present invention; and

[0010]FIG. 3 is a view similar to FIGS. 1A and 2 of a further embodiment of the fabric of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0012] Referring now more particularly to the drawings and specifically to FIG. 1, there is illustrated a fabric, generally indicated at 10, which includes warp yams 11 of continuous filament synthetic material of a denier appropriate for use of the fabric 10 as a substrate for a single ply roofing membrane. Such yam size may be within the range of 750 to 1250 denier, with 1000 denier being most preferred. The continuous filament synthetic material may be any material suitable for use in roofing membranes, examples of which are high tenacity low shrink polyester, polyamide or nylon, and fiberglass. High tenacity low shrink polyester is most preferred.

[0013] Fabric 10 also includes weft yams 12 also of continuous filament synthetic material of a denier appropriate for roofing membranes. Such weft yams 12 may be of the same denier as warp yams 11 or of a different denier. As with warp yams 11, weft yams 12 are preferably of 1000 denier. Weft yams 12 may also be of the same continuous filament synthetic material as warp yams 11 or of a different material. Most preferably, weft yams 12 are also of high tenacity low shrink polyester.

[0014] It has been determined that the addition of even a small amount of twist to the warp yams 11 and/or to the weft yarns 12 yields considerable increase in tear strength in the roofing membrane. Also, the addition of twist in the warp yams 11 or in the weft yams 12 or in both yields substantial improvement in tear strength uniformity. Accordingly, in those roofing membranes, such as in the wider membranes as opposed to narrow versions, it is preferred that warp yams 11 and/or weft yarns 12 have twist added thereto. It is believed that such twist should be at least 1.5 turns per inch, with the specific twist used being determined by the increase tear strength desired and by economics. Twist of 2.5 turns per inch is preferred.

[0015] The present invention also provides a solution to the problem of edge curl in weft insertion warp knit fabric for single ply roofing membranes, such as fabric 10. Accordingly, fabric 10 includes knit yams 13 warp knit in a predetermined stitch pattern through the warp yams 11 and weft yams 12 to bind the warp and weft yams 11 and 12 together at the points of contact or crossing thereof. Knit yams 13 may be monofilament or multi-filament yams of a synthetic material suitable for roofing membranes, such as polyester, polyamide or the like. Also, knit yams 13 may be of any suitable denier, with 70 denier being preferred.

[0016] The predetermined stitch pattern in which knit yarns 13 are warp knitted is preferably a chain stitch pattern, illustrated in FIG. 1A, where fabric 10 is to be used in roofing membranes where edge curl is a problem or of concern. In those instances where edge curl is not a major concern but tear strength is a matter of concern, then fabric 10 should include twisted warp yarns 11 and/or twisted weft yarns 12, but may have a stitch pattern other than a chain stitch pattern, such as a tricot stitch pattern, for example. Similarly, in those instances where uniformity of tear strength is not a matter of concern, but edge curl is, then fabric 10 should be formed using a chain stitch pattern in knit yarns 13, but may include untwisted warp yarns 11 and weft yarns 12, as is illustrated in FIG. 1.

[0017] In FIG. 1A, there is illustrated an embodiment in which the weft yarns 12 have twist therein while the warp yarns 11 have no twist therein and with warp knit yarns 13 binding the warp and weft yarns 11 and 12 together. Similarly, in FIG. 2, there is illustrated another embodiment of fabric 10 in which the warp yarns 11 have twist therein while the weft yarns 12 have no twist therein with warp knit yarns 13 binding the warp and weft yarns together. Finally, in FIG. 3, there is illustrated a fabric 10 “in which both warp yarns 11” and weft yarns 12 “have twist therein with the warp knit yarns 13” binding the warp and weft yarns together.

[0018] Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

That which is claimed:
 1. A fabric substrate for use in a roofing membrane comprising: warp yarns of synthetic material suitable for use in roofing membranes extending longitudinally of said substrate, weft yams cross-laid onto said warp yarns and formed of a synthetic material suitable for use in roofing membranes, and binder yams warp knit in a chain stitch pattern through said cross-laid warp and weft yarns to bind said warp and weft yarns together, whereby edge curl in said substrate is substantially elminated.
 2. A fabric substrate according to claim 1 wherein said warp yarns are formed of a synthetic material selected from the group of polyester, polyamide and fiberglass.
 3. A fabric substrate according to claim 1 wherein said weft yarns are formed of a synthetic material selected from the group of polyester, polyamide and fiberglass.
 4. A fabric substrate according to claim 2 wherein said werp yarns are formed of high tenacity, low shrink polyester.
 5. A fabric substrate according to claim 3 wherein said weft yarns are formed of high tenacity, low shrink polyester.
 6. A fabric substrate according to claim 1 wherein said warp yams and said weft yarns are formed of high tenacity, low shrink polyester.
 7. A fabric substrate according to claim 1 wherein warp yarns are of a denier within the range of about 750 to about
 1250. 8. A fabric substrate according to claim 1 wherein said weft yams are of a denier within the range of about 750 to about
 1230. 9. A fabric substrate according to claim 1 wherein said warp yams and said weft yams are of a denier within the range of about 750 to about
 1250. 10. A fabric substrate according to claim 1 wherein said warp yams and said weft yams are about 1000 denier.
 11. A fabric substrate according to claim 1 wherein said weft yams have a twist of at least about 1.5 turns per inch therein.
 12. A fabric substrate according to claim 1 wherein said warp yams have a twist of at least about 1.5 turns per inch therein.
 13. A fabric substrate according to claim 1 wherein said warp yams and said weft yams have a twist of at least about 1.5 turns per inch therein.
 14. A fabric substrate for use in a roofing membrane comprising: warp yams of a synthetic material suitable for use in roofing membranes extending longitudinally of said substrate, weft yams cross-laid onto said warp yams and being formed of a synthetic material suitable for use in roofing membranes, at least one of said warp yams and said weft yams having a twist of at least about 1.5 turns per inch for more uniform and increased tear strength, and binder yams warp knit through said cross-laid warp and weft yarns to bind said warp and weft yarns together.
 15. A fabric substrate according to claim 14 wherein said weft yams have said twist therein and said warp yarns have substantially zero twist therein.
 16. A fabric substrate according to claim 14 wherein said warp yams have said twist therein and said weft yams have substantially zero twist therein.
 17. A fabric substrate according to claim 14 wherein said twist is about 2.5 turns per inch. 